1. Field of the Invention
The present invention is related to a planar helix antenna with two frequencies, and especially to an antenna with the performance of dual frequency only by a planar helical structure.
2. Description of the Prior Art
It is the primary antenna type having a helical coil made from winding of a metal wire, diameter and material of the coil as well as the total length of such a helix antenna can influence the set functions thereof. However, such a helix antenna still is widely adopted and has a quite stable signal emitting and receiving structure. In meeting the requirement of modern communication equipment, such a helix antenna can get various resonance frequencies through different structural designs. For example, Japanese patent No. 1997-320748 has a helical coil provided in an external sleeve, and an adjusting member is extended in the external sleeve, length of the adjusting member determines its resonance frequency. British patent No. 2,206,243 has a linear conductor extended into a helical coil to form a dual frequency antenna. These helical coils are disadvantageous in being geometrically solid and having larger volumes though, they do not certainly suit modern communication equipment that is miniature and is supposed to use a built-in antenna (such as a mobile phone or a portable computer).
Thereby, there are various miniaturized and planar microstrip antennas being developed gradually. However, earlier microstrip antennas, such as are disclosed in U.S. Pat. No. 3,921,177 and 3,810,183, generally are made from round or rectangular thin metallic rods, dielectric substance is filled in the space between such an antenna and the grounding member. Such a microstrip antenna generally can only allow narrower width of frequency. U.S. patent application Ser. No. 07/695686 provides a polygonal helical microstrip antenna which is improved against the earlier microstrip antennas, the width of frequency thereof can approach that of a normal helix antenna with a constant impedance. But this microstrip antenna is disadvantageous in having quite a large diameter when in low frequency, and does not suit modern portable communication equipment.
Pointing to this, U.S. patent application Ser. No. 07/798700 (Taiwan patent no.81108896) provides a smaller microstrip antenna of broadband. However, the helical antenna element thereof is provided on a grounding plate, and dielectric substance and bearing material are filled in the space between it and the plate; the antenna can hardly further be reduced, and its signal emitting and receiving function is inferior to that of a helix antenna.
The object of the present invention is to provide a planar helix antenna with two frequencies; the performance of a dual frequency antenna can be achieved by a planar helical structure.
To get the object, the present invention is provided on both the upper and the bottom sides of an electric circuit board with corresponding microstrip antenna sections, these microstrip antenna sections on the front and the back sides can cooperatively form a helix antenna, through holes are provided on the circuit board for the conjunction ends of the microstrip antenna sections for electric connection. The top most end of the microstrip antenna sections has top loading, by setting spaces between the microstrip antenna sections, the planar helix antenna can get a high frequency harmonic oscillation point by coupling; while connection of these microstrip antenna sections on the front and the back sides can form a low frequency harmonic oscillation point by its electrical gross length.
The present invention will be apparent in its novelty as well as features after reading the detailed description of the preferred embodiment thereof in reference to the accompanying drawings.